Electrode for electric discharge devices



July 5, 193s.

E. R. PloRE Er AL 2,123,024 ELECTRODE FOR ELECTRIC DISCHARGE ,DEEVIGEISk Filed May 29, 193s t Louis Malter M Gttorneg nieuwe .my s, yuns f UNITED STATES anaest- PA'rENT-v OFFICE' ELECTRODE FOB EDECTRIC DISCHARGE DEVICES 1 Emanuel lt. Piore, Philadelp Pa.. and Louis )Kalten Oaklyn, N. J., asaignors to Radio Cor. poration of America. a corporation of Delaware Application May zo, massaal No. n.452 schaun.- wieso-#215) This invention relates to electric discharge devices, particularly to electrodes therefor, and has for its principal object the provision of an electrode having improved photo-sensitive and secg ondary-electron emissive characteristics.

Other objects will be apparent and the invention itself will be best understood by reference to the'foliowing specification andto lthe accompanying drawing, wherein:

1o Fig. 1 is a diagrammatic view of an electron multlplierf system wherein an electrode constructed in accordance with the invention may proposed to oxidize the metal and to treat the l oxidized surface with caesium, rubidium, sodium, or other electro-positive metal. A secondaryelectron emissive constant of 'l to 9 is obtainable f" with caesium on oxidized-silver: rubidium on oxidized silver will provide an emissive ratio of substantially 6.5 to 8.5 secondary electrons to each impinging electron.

In constructing electrodes of the type described, the preferred practice is to mount the clean metal electrode structure in the tube and. after evacuation, to introduce oxygen into the.y tube. The oxygen is activated orionized, as by the application of an externally applied high frequency neld and, thus activated. combines readily with the electrode metal. When oxidization has been completed the tube is re-,evacuated- Caesium, which may be contained Lin the form of pellets within an auxiliary container connecting with the tube contai the electrodes. isvaporized as by the applicationo heat and the resultingvaporenters'into the main tube and combineswith the A oxidized metal to render it emissive. ExcessiveJ caesium isremoved or "taken-up," within the tube. The tube is baked, on the pump; and the l sealing-in operation completed.

'I'he4 present invention contemplates and its practice provides a metal electrode which has not only been oxidized'and treated (as with caesium) I. but also re-oxidised and retreated witlr the same nalkali metal. The metal whose surface is to be rendered emissive is selected from the group of metals whose oxides have a `heat of formation',1

per oxygen bond, of .the 'same'or substantially Il the same order as that of the metallic element with which it is treated. Thus, whereas the prior art dictates the treatment of silver (whose oxide has a -heat of 4formation of the order of 5000 calories per mol.) with a single application of caesium (whose oxide hasla heat of formation l,

- of substantially 88,000 calories per mol.) the present invention involves a double application of caesii'im,y or the like (with the introduction of oxygen between these applications), to a metal whose oxide has a heat of formation of the same 10 order o f magnitude as that 0f caesium.

Among the metals whose emissive characteristics .may be enhanced by the improved method of my invention are beryllium, zirconium, molybdenum. columbium and zinc. The heat of forl5 mation of the oxides, per oxygen bond, of these metals is of the order of 80,000 to 90,000 calories per mol. The alkali metals preferably employed in treating the `above mentioned metals are cae-v sium, rubidium, and zpotassium. The heat of '20 formation of the oxides of these metals are, respectively, 88,000, 88,500, and 86,800. Sodium whose oxide has a heat of formation of substantially-100,000 may be included in this group.

yI n carrying the invention intoeil'ect the elec- 25 trode to be treated is first pre-oxidized, either electrolytlcally before it is mounted in the discharge tube, or by an oxygen glow discharge within the tube itself, or it may be oxidized within or without the tube in any known manner. Pref- '3o erably this oxide coating is of a thickness of they order of, say. three hundred atomic layers. 'With the oxidized electrode surface or surfaces mounted within the tube, the tube is highly evacuated and a substantiaiamount of caes'ium, or like al- 35 kali metal, is distilled into it. preferably in the manner previously described. The excess `cae-- slum or other vapor is removed as by baking at 'a temperature of 200 P. for about ten minutes with the tube o'n the pump. admitted and allowed to remain in the tube for. say three minutes, until it has reacted with the caesium to form a layer of a mixture constituted of an oxide of caesium 'and the oxide o! the metal of which the base is formed.. The tubeis then reexhausted, after which the electrode is again bathed in the alkali metal vapor. This' second bath o! metal vapor forms a molecular layer of thealkali metal on the siirface of the "mixed oxide layer". The excess metal vapor isremoved i0 by baking and pumping, as before, and thetube is then sealed oil. I

f Referring now to Fig. l of the drawing inwhich electrodes'formed in accordance with the invention are utilised in an electron multiplier plying electrode.

`cathode in random directions.

device of a' known type. The device comprises a Y-shape evacuated container I, within which, adjacent the closed ends of one of its arms, is mounted a photosensitive cathode 3 and adjacent theclosed end of the other of its arms is an output electrode 5. A third electrode 1 is mounted between `the input and output electrodes 3 and 5 in the angle or stem of the Y-shape container l. Both electrodes 3 and I are constituted in accordance with the invention of a metal base having a mixed oxide coating and a layer of alkali metal superimposed on this coating. The output electrode 5 may be of nickel or other suitable material.

A variable or a constant lightsource may be so disposed with respect to the container that light therefrom falls upon the photosensitive cathode. In the drawing, such light source is exempliiled by a lamp 8 connected'in circuit with a battery 9 and a variable rheostat II, and a lens I3.

Under the influence of light from the source, electrons leave the surface of the photosensitive Since it isdesirable to focus all suchelectrons upon the multl, plying electrode an electromagnetic coil I5 may be disposed around one arm of the container between the photo-,sensitive cathode and the multi- A similar coil I 'I imay be disposed around the other ,arm of the container for the purpose of focusing secondary electrons upon the output electrode.

The several focusing coils may beprovided with unidirectional potential from a battery I9 or the like. In the drawing these coils are exemplified as being connected in parallel to the battery,\ a potential divider 2| and a plurality of contact' devices 23 and 25 being'utilized for the purpose of individually controlling the magnitude of the several focusing field currents. It is our understanding that the polarity of the coils is immaterial. A1ternative1y,`.` electrostatic focusing o'f the electrons may be resorted to, or a combination of electrostatic and magnetic focusing.

In the operation of an electron multiplier of thetype under discussion the output electrode 5 may be connected to any suitable utilization circuit, such as a relay21. When utilizing a multiplier of the type shown, the photosensitive-cathode may be connected tothe negative terminal of a potential divider 29 that connected across a source of unidirectional potential 3l, the output electrode 5 connected to the positive terminal of the potential divider and thev multiplying electrode 'I connected to an intermediate point thereon. The relative .potentials shown in rthe drawing are to be construed solely as illustrative.

f siumvon said layer.

Referring to Fig. 2, the base lupon which the mixed oxide layer and the alkali metal coating is applied may be it mere sheetvof beryllium intimately iointed, as by evaporation, to a base of another and cheaper metal, such for instance as nickel. Such construction is recommendedl where the metal to which the mixed oxide layer and alkali metal `coating is applied is not available in sheet form.

As indicated in both Figs. 1 and 2, when the electrons constituting the primary beam from the cathode strike the composite electrode surface with sufficient energy, secondary-electrons are emitted. The electrons, so released are drawn to the collector electrode, or if desired to another similar surface for further multiplication by reason of the electric field applied between the emitter and the target electrode.

While the invention has been described in connection with a photo-actuated electron-multiplier tube, it is to be understood that its application is not to be limited tothe particular type of tube here described, as the disclosure, in this respect, is merely illustrative for purposes of explaining the inventive concept.

What is claimed is:

1: An electrode comprising a metal base having thereon a layer of a mixture of an oxide of said metal and an oxide of an alkali metal whose oxide has a heat of formation, per oxygen bond, of substantially the same order as that of the oxide of the metal constituting said base, and a coating of said alkali metal superimposed on said layer.

2. An electrode comprising a base of a metal whose oxide has a heat of formation, per oxygen bond, of the order of substantially 80,000 to 90,000

calories per mol., a layer on said base constituted of an' oxide of said metal and an oxide of an alkali metal Whose oxide has a heat of formation, per oxygen bond, of the order of substantially 80,000 to 100,000 calories per mol., and a surface coating of said alkali metal on said layer.

3. An electrode comprising a base of beryllium, a layer on said base constituted of beryllium and casesium oxides and a surface coating of caesium on said layer.

4. An electrode comprising a base of beryllium, a layer on said base constituted of beryllium and rubidium oxides and a surface coating of rubidium on said layer.

5. An electrode comprising a base of beryllium,

a layer on said base constituted of beryllium `and f potassium oxides and asurface coating of potas- EMANUEL' R. PIORE. LOUIS MALTER. 

